In railroad locomotive operations, the throttle, dynamic brake and reverser actions of the locomotive, locomotives or other drive units, are controlled by the operator or engineer in the cab of the lead unit by manipulating three handles extending from the control stand, one handle each for throttle, dynamic brake, and reverser. The throttle handle, of course, controls the development of the tractive effort of the locomotive; i,e, the diesel engines or other power units. The dynamic brake handle controls the development of a retarding force known as a dynamic brake, for example the electric motors driving the locomotive wheels, to place them in either motor mode where they will drive the wheels, or in generator mode, where they will function as a retarding force. The reverser handle controls the forward and reverse rotation of the electric motors to selectively drive the train forward or rearward, and includes a neutral position. Pursuant to current practice, the control stand is designed to be a man-to-machine interface and ideally is strictly an electronic/electric device having no direct mechanical, hydraulic or pneumatic connections to the devices controlled. Instead, encoding means are preferably provided within the control stand to read and interpret the positions of the three handles, and convey appropriate signals, indicative of such positions, to an associated microcomputer. The associated microcomputer is programmed to interpret the encoded signals regarding the positions of the throttle, dynamic brake and reverser handles, as positioned at the control stand, and then electronically issue corresponding commands to manipulate the devices intended within the locomotive or locomotives. When utilizing a microcomputer, the throttle, dynamic brake and reverser commands effected at the control stand, are dependent upon the given angular positions of the three control handles, which are normally sensed and monitored by rotary encoding devices, which are mechanically coupled to associated rotary axles to which the control handles are secured, utilizing cams to actuate microswitches or contacts to provide a signal to the microcomputer as noted above. Such mechanical devices leave a lot to be desired, in that they do not provide the exacting degree of handle position determination as desired, are prone to mechanical failure, are cumbersome, space consuming, and require frequent adjustment.
It has of course been highly desirable to provide an interlocking mechanism within the control stand to prevent certain handle movements which are inconsistent with the intended results, such as simultaneously requiring throttle and dynamic brakes actions, or application of the dynamic brake when the reverser is in neutral. While a variety of such interlocking mechanisms have been utilized in the prior art control stands, most tend to be rather complicated, utilizing a significant number of moving parts which greatly complicate assembly of the control stand, and lead to limited durability and reliability.
Co-pending patent application titled: Apparatus For Interlocking Throttle, Dynamic Brake and Reverser Handles on a Control Stand of a Railway Locomotive, Ser. No. 08/340,215, filed Nov. 16, 1994, and assigned to the same assignee, discloses and claims apparatus for interlocking independent control handles for throttle action, dynamic brake action and reverser action, within a control stand for a railway locomotive which effectively interlocks the throttle and dynamic brake handles to each other and to the reverser control handle as necessary permitting only allowable motions of the three handles. The above co-pending patent application does not, however, include any interlocking means for permitting removal of the reverser control handle, which is another desired and common feature. That is to say, it is further common practice to permit the reverser control handle to be removable from the control stand by the operator or engineer to essentially lock-out the control stand, as for example, when he leaves the cab, to thereby assure that if an unauthorized person thereafter enters the cab, that such person will not be able to operate the control stand. In this regard, it is further essential that interlocks be included to assure that the reverser control handle be removable only when the throttle and dynamic brake are inactive, that is, when the dynamic brake is in the "off" position, the throttle is in the "off" or "idle" position, and the reverser is in the "neutral" position.
Since all three of the above conditions must be met to permit removal of the reverser control handle, interlocking apparatus of the prior art was rather complicated, often time including three separate locking means, each of which have to be interlocked to recognize the position of one each of the other handles, and thereby maintain or release the lock in responses to such three separate determinations.